There seems to be a word missing between "she" and "on."

Masami's comment is a reasonably good answer. Your sentences are not correct, as there is something missing. You need some sort of verb phrase after 'as she'. The form should be something like "Someone did something as they did something else." Her first two examples are not quite right though, as they need another 'as' before 'tightly'. Another one is: Annette grasped the racket tightly as she walked onto the tennis court

First correction: Are these sentences correct? As for the two sentences stated, I am not sure of the exact statement/idea that you are trying to construct. POSSIBLE SENTENCES: Annette held the racket tightly as she could on the tennis court. Annette grasped the racket tightly as she could on the tennis court. Annette grasped/held the racket tightly when she was on the tennis court.